Yellow Oxide in Oil will also be found in the oil color lists of some manufacturers, but the demand is rather limited. There are some very pretty yellow oxides offered to the trade from English and Italian sources, and there is a limited quantity found in this country. Color grinders use yellow oxides to strengthen ochers that are listed under fancy names; also to mix with raw sienna. The percentage of oil required for grinding yellow oxides varies to some extent, the English variety needing 30 pounds oil to 70 pounds dry pigment, while Sardinian yellow earth (oxide) requires 38 to 40 pounds of oil for 60 to 62 of pigment. Very bright yellow oxides are very useful in making pigment stains, as well as for tinting. In that case and when wanted for that purpose they should be ground very fine in strong boiled oil.
Next and of not less importance in the line of yellow pigments are the Chrornate of Lead Yellows. Here we have the pale or light shades, usually designated as lemon, citron or canary yellow, then the medium or, as the English call it, middle chrome yellow, which is or should be the neutral or normal lead chromate, and which is sometimes deeper, sometimes lighter, according to the luck the color maker has in perfecting the batches; then comes the deep or orange chrome yellow, to which some color makers add another darker shade which they term D. D. chrome or D. orange chrome yellow. When it comes to the very deep orange shade, the output of these varies with almost every color maker's product. The pale shades, that are designated as canary, citron, lemon or primrose yellow, according to their tone, vary to quite an extent, even when pure, in strength as well as in their absorption of oil on grinding, and we have noted formula labels on cans of pure lemon chrome yellow where the percentage given was 86 per cent pigment to 14 per cent oil. If correct, this statement would indicate that this yellow, although free of adulterants in the strict sense of the term, contained an excessive portion of lead sulphate, probably basic lead sulphate in the form of added sublimed lead. A normal basic chromate of lead of the lemon or primrose shade should not contain over 40 per cent of lead sulphate, which is necessary, in connection with the bichromate of potash or soda, to produce the pale shade, while a canary shade may contain more. The percentages of pigment and oil in these should not vary more than 2 or 3 points; in other words, 77 to 80 per cent pigment and 20 to 23 per cent of oil should constitute a good, workable paste. The oil used in mixing and grinding should be bleached or clarified, and the color grinders in selecting the dry yellow should guard especially against the use of any that contain any portion, no matter how small, of alumina hydrate; which is used in the chrome yellow for printing ink and wall paper printing successfully, but causes trouble by livering for the painter. Other points to be considered are that the yellow selected is of good tone, as rich as may be had, soft in texture and of standard strength, most of it being used for tinting or mixing with other pigments, as, for instance, in greens, where the medium chrome yellow would produce too much of an olive effect. This is obvious when it is known that the chrome greens are mixtures of lemon chrome and Prussian blue, as these could not be obtained by mixing the medium chromes with the blue.
Medium Chrome Yellow in oil is most used in point of quantity by the general painting trade, on account of its great tinting power and brilliant yellow color. The various brands of chemically pure medium chrome yellow vary to quite an extent in these points, although there has been a general improvement all along because of competitive tests made by master painters' associations and by the salesmen representing the manufacturers. The color grinder, who at the present time places second or third grade of this yellow on the market to supply a demand for low price, is not afraid to let this fact be known, and the consumer is not kept in the dark although there may be some exceptions. The extending material for medium chrome yellow in such cases would be principally barytes, although whiting, gypsum, clay or floated silex may be used, so as to give bulk. The oil, when quoted as at present, being not much more than one-half of the cost of the pure medium yellow, does not cut so much of a figure as it did a few years since. The proportions for mixing and grinding a normal medium chrome yellow in oil should be 74 per cent by weight of dry pigment and 26 per cent by weight of bleached or clarified oil, but when raw linseed oil is specified as the vehicle it may require 28 per cent of oil, and under certain conditions, as, for instance, in the case of a very fluffy yellow, 30 per cent of oil and 70 per cent pigment will still produce a paste that cannot be condemned as too liquid. When the color grinder intends to supply a demand for "extended" or "stretched" medium chrome yellow, a 40 per cent article would still produce a paste that, when thinned for a body or trimming color, will cover up solid in one coat over the right ground. A good formula for this is as follows: - Thirty pounds chemically pure medium chrome yellow, 45 pounds finest blanc fixe, 25 pounds clarified oil. Another, showing more strength in tinting, fair body, but not as good spreading capacity as the former, is: - Thirty pounds chemically pure medium chrome yellow, 52 pounds floated natural barytes, 18 pounds clarified oil. Still another, more bulky than the last, lower for cost, but of less strength and hiding power, is as follows: - Twenty pounds medium chrome yellow, 30 pounds bolted china clay (best English), 30 pounds floated barytes, 20 pounds bleached linseed oil. This may look like a very cheap dope, but it is really good for solid painting, alongside of some of the medium chrome yellow that has been found from time to time on dealers' shelves. The formulas here given no grinder need be ashamed of, when low-priced goods are demanded; it is only the deception that has been practiced years ago that creates suspicion of improper business practices. In selecting his dry medium yellow the color grinder looks for richness of tone, fineness, softness of texture, and, above all, tinting power, and it is really a matter of indifference to him whether the pigment is a nitrate or an acetate of lead yellow, or whether it is made with bichromate of potash or sodium bichromate. Exposure tests of yellows made either way in comparison with one another have shown very contradictory results, and it looks very much as if the permanency of the yellow to strong light or atmospheric conditions depends to a great extent on the mechanical side of the process, i. e., the proper way of treating a batch from end to end, temperature of the water, and the final washing of the color. The color grinder, too, must guard against overheating of the yellow in mixing and milling, and select mills of slow speed for this pigment.
Orange Chrome Yellow in Oil is in fair demand, but mostly that of the light shade, that is, next in depth to the medium yellow. The yellows of this type take the least percentage of oil for grinding of all chrome yellows, and the darker the shade the less is the percentage of oil required in the grinding. Thus, while a rather pale shade of orange chrome requires 20 pounds oil to 80 pounds pigment, a neutral shade requires only 18 pounds oil to 82 of dry color, and in the dark shades of orange it runs from 15 to 17 pounds of oil for 83 to 85 pounds dry color, when chemically pure color is considered. As for the extended brands, the same method for reducing cost is suggested as that for medium chrome yellow. There is a demand for body colors of these types, and on account of the necessity for frequent repainting, because of the darkening of the yellow by the sulphur gases in the air, etc., those favoring the color do not care to pay for chemically pure material when this will do no better than the extended material and probably not as well. Magnesium silicate (asbestine) also suggests itself as an extender, but as it is always slightly alkaline it had best be omitted in paste containing yellow of the lead chromate type, which is very sensitive to the action of even weak alkalies. When grinding bases with chrome yellow, be it light, medium, dark or dark orange, for dipping paint for implement or wagon work, it is best to use as much zinc oxide as the shade is able to stand without losing its yellow or orange effect, and as much pure whiting (that is previously tested with litmus paper for alkaline reactions) as possible, and a moderate portion of china clay of fine quality. Here is a formula for a paste that has given excellent results when thinned with ordinary painters' naphtha (62 per cent benzine) and benzine drying japan: - Fifteen pounds dark chrome yellow (orange), 5 pounds American zinc oxide, 40 pounds Cliffstone bolted whiting, 20 pounds English china clay, and 20 pounds raw linseed oil, ground fine on esopus stone mills of 30-inch diameter.
Paste Yellows in Oil for the implement and wagon manufacturing concerns, for both dipping and brush work, are not based, as they used to be in the past, on French yellow ocher tints, but are now so standardized that only chrome yellow of light, medium or dark shade can be employed in coloring the white base, that may be lead carbonate and zinc oxide or basic lead sulphate (sublimed lead) and zinc oxide extended or zinc lead, leaded zinc or lithopone, although the last named must not be used in connection with lead chromate. These bases are, as a rule, made to match a standard sample or to specifications, and therefore it is scarcely worth while to give more than one specimen formula here. Such a one is as follows: - Twenty-five pounds dry white lead or sublimed white lead, 25 pounds zinc oxide white (American), 25 pounds English Cliffstone Paris white, not over 5 pounds chrome yellow, ground to a medium paste in 16 pounds raw linseed oil of best quality and 4 pounds turpentine drier.